Magnetrons having cyclically varying frequencies



April 29, 1969 y B. F. COOPER 3,441,796

MAGNETRONS HAVING CYCLICALLY VARYING FREQUENCIES Filed July 20, 1966 k h l Ill INVENTOR BRIAN FREDERICK COOPER ATTORNEYS United States Patent 3,441,796 MAGNETRONS HAVING CYCLHCALLY VARYING FREQUENCIES Brian Frederick Cooper, Essex, Engiand, assignor to English Electric Valve Company Limited, London, England, a British company Filed July 20, 1966, Ser. No. 566,612 Claims priority, application Great Britain, Aug. 9, 1965, 33,991/ 65 Int. Cl. Hillj 25/50 U.S. Cl. 31539.61 9 Claims ABSTRACT OF THE DISCLOSURE A strapped magnetron having each one of a pair of alternate anode connecting straps provided with discrete surfaces to cooperate with the surfaces of the other of the pair to constitute inter-strap capacitances. The magnetron is provided with a rotor having discrete conductive parts arranged so that, upon rotation, the parts traverse the dielectric spaces of, and vary the values of, the capacitances.

widespread use at present. In a strapped magnetron alter- 4 nate anodes are connected together by at least one connection and the remaining alternate anodes are connected together at least by another connection. These connections are known as straps and in the most widely used strapped magnetrons they are in the form of arcuate connections at the end or ends of the anode block (commonly at both ends) each connection being usually in the form of a ring concentric with the axis and connected to the alternate anodes which it straps together. However, any connection strapping together alternate anodes may be termed a-strap. The oscillating frequency of a magnetron operating in the mode depends inter alia upon the capacity between the pair of straps one of which connects together one set of alternate anodes and the other of which connects together the other set of alternate anodes. The present invention takes advantage of this fact to provide improved rapidly tunable magnetrons.

According to this invention each of a pair of alternate anode-connecting straps of a magnetron is provided with a plurality of discrete surfaces positioned to cooperate with the surfaces of the other to constitute a plurality of inter-strap capacitances distributed along the strap length and a rotor having a plurality of discrete conductive parts is so mounted and arranged that, upon rotation, said parts in turn traverse the dielectric spaces of said capacitances to vary the values thereof as they pass.

Preferably each of the straps is provided with the same number of projecting teeth, those on one strap projecting towards those on the other. The rotor may have the same number of teeth each of which, when aligned with and between two opposed teeth, one on each strap, almost fills the space between said two opposed teeth but contacts with neither. Alternatively the rotor may have the same number of holes each of which, when aligned with and between two opposed teeth, one on each strap, leaves the space between said two opposed teeth, unobstructed, the material between adjacent holes being able to pass between said teeth without contacting with either. The two straps may be rings mounted outwardly of one end of the magnetron anode block in planes perpendicular to the magnetron axis with the teeth projecting in directions parallel to said axis, the axis of rotation of the rotor being coincident with said axis. Alternatively the two straps may be sleeve shaped and mounted outwardly of one end of the magnetron anode block, with teeth projecting radially with respect to the magnetron axis, the axis of rotation of the rotor being again coincident with said axis.

Preferably the rotor and the bearings therefor are inside the evacuated envelope of the magnetron, the rotor being adapted to be rotated by a rotating magnetic or electromagnetic field applied by means lying outside the envelope.

It is possible to provide capacitance straps and an associated rotor, arranged in accordance with this invention, at both ends of the anode bloc-k but it is preferred to provide such an arrangement at one end only, and to provide straps of usual known construction and arrangement at the other end of the block.

The invention is illustrated in the accompanying drawings in which:

FIGURE 1 shows one embodiment, and

FIGURES 2, 3 and 4 show another embodiment.

The drawings are diagrammatic and show the respective magnetrons to which they relate only to the extent necessary for an understanding of the present invention.

FIGURE 1 is a diagrammatic diametrical view of a magnetron in accordance with this invention, cut diametrically through the anode block. Referring to FIGURE 1 the customary central cathode is represented at 1, 2 being the usually so-called end hats. The magnetron illustrated is of the vane type and has an anode block comprising radial vanes of which two appear at 3. At one end of the anode block are two ring straps 4 and S of usual construction and arrangement, the strap 4 interconnecting one set of alternate vanes (anodes) and the strap 5 interconnecting the other set of alternate vanes.

At the other end of the anode block alternate vanes are connected through connecting posts 6 to a metal ring 7 and the remaining alternate vanes are connected through metal connecting posts 8 to a similar metal ring 9. The rings 7 and 9 are spaced apart and lie in planes perpendicular to the axis of the magnetron which is the axis of the cathode structure. Each of the rings 7 and 9 is provided with a like plurality of teeth 10 or 11 which project towards one another in directions parallel to the magnetron axis and are situated opposite one another. As will be apparent each pair of opposed teeth provides a capacitance, the spacing of the electrodes of which is the spacing between the adjacent ends of said teeth. Between the two rings 7 and 9 is mounted an annular disclike rotor portion 12' of conductive material. The rotor, generally referred to by the numeral 12 and including each of the rotatable parts within the envelope 20 connected with the rotatable disc 12', is mounted in bearings providing an axis of rotation coincident with the magnetron axis. The rotor portion 12 is provided with the same number of teeth 13 as there are on each of the rings 7 and 9, each tooth projecting from both sides of the rotor so that when the said rotor is in the position shown in FIGURE 1 and each of its teeth is aligned between a pair of opposed teeth, one on each of the rings 7 and 9, the capacitance between said opposed teeth is materially changed by the presence of the rotor tooth. Outside the envelope 20 of the magnetron-all the parts so far described are inside the envelope-are suitable means (diagrammatically illustrated at 21 in FIGURE 1) for providing a rotating magnetic or electromagnetic field which will penetrate the envelope 20 and the rotor is suitably constructed to be rotated by the field (as diagrammatically illustrated in FIGURE 1 by the inclusion of a portion 22 of the rotor 12 within the rotating magnetic field). In this way there is avoided any need for a mechanical drive through the envelope of the magnetron to rotate the rotor. While the function of the magnetic or electromagnetic driving provisions has been indicated by the illustration of rotating magnetic poles at 21 in FIGURE 1 and a portion 22 of the rotor 12 positioned within the rotating magnetic field, a convenient drive arrangement comprises a three-phase winding outside the envelope, the rotor being, in effect, the rotor of a conventional eddy current AC. motor conventionally employed to effect rotation of a conductive disc-like rotor.

It will be seen that in the arrangement of FIGURE 1 when the teeth of the rotor lie between the teeth on the rings 7 and 9 the inter-strap capacity--the straps are constituted by the rings 7 and 9will be at a maximum and the oscillation frequency of the rotor will therefore be a minimum. When the rotor position is such that its teeth are halfway between successive pairs of opposite teeth on the rings 7 and 9 the inter-strap capacity will be at a minimum and the oscillating frequency will be at a. maximum. It will also be seen that the invention provides the great advantage that for each rotation of the rotor there will be a number of cycles of frequency change equal to the number of teeth in the rotor-assuming that the rotor and each of the two rings has the same number of teethand accordingly the number of cycles of frequency change in each rotation of the rotor can be made very large indeed. A high rate of tuning variation may therefore be obtained with only a relatively small speed of rotation of the rotor.

Instead of employing a toothed rotor, a rotor with holes in it may be used. A construction of this nature is shown in FIGURES 2, 3 and 4 in which like references denote like parts in FIGURE 1. FIGURE 2 is a diagrammatic view of the same nature as FIGURE 1 while FIG- URES 3 and 4 are part-views to a larger scale.

Referring to FIGURE 2 there is provided at one end of the anode block a sleeve-like outer strap 17 having spaced teeth which in this case project radially inward. FIGURE 3 shows part of the strap 17 with its teeth 10 in a broken-away perspective view. The strap 17 connects one set of alternate vanes. Adjacent and inwardly of the strap 17 is a similar sleeve-like strap 19 which connects the remaining alternate vanes of the magnetron. The strap 19 has radially projecting teeth 11' on its outer surface, each tooth 11' being opposite a tooth 10. Projecting down between the teeth is the open end of a sleevelike rotor 112 which has as many holes 13 (in the form of rectangular slots) as there are teeth in each of the straps 17 and 19. The slots 13 are arranged in a ring round the rotor 112the rotor is shown in broken-away perspective view in FIGURE 4and the arrangement is such that in one position of the rotor each of the teeth 13 lies between an opposed pair of teeth 10', 11. The straps 17 and 19 and the rotor 112 are all coaxial, the axis of rotation of the rotor being coincident with the axis of the magnetron. As will be apparent, in the arrangement of FIGURE 2, the inter-strap capacity is at a minimum when the holes 13 are radially aligned with the teeth 10 and 11 and at a maximum when each of said holes is midway between two successive pairs of opposed teeth.

I claim:

1. A strapped magnetron comprising a cathode, an anode having cavity defining projections thereon, anodeconnecting straps connecting together alternate ones of said projections, said straps having capacitance means thereon for providing inter-strap capacitances distributed along the length of said straps and including discrete opposed surfaces on each of said straps, a rotatable rotor having a plurality of capacitance varying discrete conductive parts thereon positioned between said straps for movement with rotation of said rotor to vary said interstrap capacitances during movement thereof.

2. A magnetron as claimed in claim 1 wherein each of the straps has thereon a number of projecting teeth, each strap being provided with the same number of projecting teeth, the teeth on one strap projecting towards the teeth on the remaining strap.

3. A magnetron as claimed in claim 2 wherein the rotor has thereon a number of teeth, the rotor and said straps having the same number of teeth thereon, said rotor teeth, when aligned with and between two opposed teeth, one on each strap, substantially filling the space between said two opposed teeth and contacting with neither of said opposed teeth.

4. A magnetron as claimed in claim 2 wherein the rotor has therein a number of holes, said rotor having the same number of holes as there are teeth in each strap, each of said holes, when aligned with and between two opposed teeth, one on each strap, leaving the space between said two opposed teeth unobstructed, the material of said rotor between adjacent holes being passable between said teeth without contacting with either of said opposed teeth.

5. A magnetron as claimed in claim 2 wherein said two straps comprise rings mounted outwardly at one end of the magnetron anode in planes perpendicular to the magnetron axis with the teeth projecting in directions parallel to said axis, the axis of rotation of the rotor being coincident with said axis.

6. A magnetron as claimed in claim 2 wherein the straps are sleeve shaped and mounted outwardly of one end of the magnetron anode, with teeth projecting radially with respect to the magnetron axis, the axis of rotation of the rotor being coincident with said axis.

7. A magnetron as claimed in claim 1, including an evacuated envelope, said rotor being rotatably mounted inside the evacuated envelope and means lying outside the envelope for applying a rotating field to the interior thereof for rotating said rotor.

8. A magnetron as claimed in claim 1 wherein said straps and associated rotor are provided at one end only of the magnetron, further strapping means being provided at the other end of the magnetron for connecting ones of said cavity defining projections at said other end.

9. In a strapped magnetron including a central cathode and an annular anode having radially inwardly projecting cavity defining portions extending toward said central cathode; strap means interconnecting ones of said inwardly projecting portions including a first member connected with a member of said inwardly projecting portions and a second member connected with a further number of said inwardly projecting portions, said first and second members being coaxial and proximate and having thereon a plurality of circularly arranged means for establishing capacitive coupling between said first and second members, said magnetron further comprising rotatable rotor means coaxially located between said first and second members and defining a plurality of circularly arranged discrete capacitance varying means movable between said first and second members upon rotation of said rotor for varying the capacitive coupling of said circularly arranged means for establishing capacitive coupling and for varying the output frequency of said magnetron a predetermined number of times per rotation of said rotor.

References Cited UNITED STATES PATENTS 3,247,421 4/1966 Backmark 31539.6l

Barbasso 31539.55 Edwards 31590 X Fracassi 31539.61 Brown 315-3969 X Hutchinson 315-39.61 Dubois 315-39.69 X

Backmark 31539.55

HERMAN KARL SAALBACH, Primary Examiner.

10 S. CHATMON, JR., Assistant Examiner.

US. Cl. X.R. 

